Electric vehicles including golf carts, automobiles, and the like, employ batteries, such as lithium batteries, that can become damaged if discharged to too low of a voltage or overcharged to too high of a voltage. Charging batteries typically involves a separate battery charger. This charger may be connected to the batteries via a power inlet and a plug attached to a cable which, in turn, is connected to the charger. A wall electrical outlet may provide a source for battery charging. Many people may forget that their vehicle is plugged in and proceed to start the vehicle and drive off; therein damaging the vehicle charging components and/or the outlet. In addition, anyone near the vehicle as the charger cord is ripped from the wall or the vehicle could be injured.
Lithium ion batteries require special controls in many applications as they require monitoring of their state of charge to ensure that they are not operated below a threshold voltage value and/or are not over charged. Lithium batteries can be irreversibly damaged if operated below a threshold voltage value. Lithium batteries may lose their ability to be fully charged if they are operated below a threshold voltage for too long. A plurality of lithium batteries would be required to generate the voltage needed for most vehicles and therefore a plurality of lithium batteries may need to be connected in series. When a plurality of batteries are coupled together, it is important to keep the level of charge of each battery within a range of the other batteries to prevent damage and to get maximum capacity.
As shown in FIG. 1, lithium batteries have a non-linear discharge profile, with a relatively flat discharge region up to about 80% discharged. Therefore, a small change in voltage can mean a large difference in the state of charge, unlike a lead acid battery that has a relatively linear drop in voltage as the battery is discharged. The state of charge of a lead acid battery, and therefore the amount of power remaining, is more easily monitored by a battery monitoring system by simply measuring the voltage of the lead acid battery. The amount of power remaining in a lithium battery system is more difficult to monitor and predict however by simply measuring voltage. It would therefore be more difficult to determine the available power remaining in a lithium battery unit by simply measuring the voltage.
Current charging systems are configured to charge a battery pack to a predetermined voltage. However, the individual batteries within a battery pack may not be charged to the same level, and the discrepancy between the batteries state of charge levels can cause capacity to be limited. The battery pack capacity is limited to the capacity of the lowest battery unit. Additionally, when a battery has a lower state-of-charge level, as the battery discharges, it may discharge to a level resulting in permanent loss of charging capacity.
Current battery management systems obtain data about individual batteries in a battery unit. The systems reserve addresses for communication with battery unit sensors and/or battery units. When sensors transmit data about battery units to the management system, the sensors include the address of the battery unit. Such a system may require significant amounts or resources and complex arrangements for connecting the components of the system.